Method of conducting electrolysis in a solid ionic conductor using an electron beam



United States Patent 3,366,562 METHOD OF CONDUCTING ELECTROLYSIS IN ASOLiD IONEC CONDUCTOR USlNG AN ELEC. TRON BEAM Abner Brenner, ChevyChase, Md, assignor to the United States of America as represented bythe Secretary of Commerce Filed Apr. 29, 1965, Ser. No. 452,034- 3Claims. (Cl. 204-164) This invention relates to electrolysis, and moreparticularly to the electrolysis of solid electrolytes by means of abeam of electrons.

It is well known that the electrons emitted by the tungsten filament ofan ordinary incandescent lamp may be used to deposit metallic sodium inthe soda glass envelope of the lamp. In the typical demonstration ofthis effect, the lamp envelope is partially immersed in a molten sodiumnitrate bath, the filament is energized, and an electronacceleratingvoltage is applied between the filament and molten bath. With a shorttime, a deposit of metallic sodium forms on the interior surface of theenvelope. The accepted explanation for the deposit is that the sodiumions in the molten bath migrate through the heated glass envelope,receive an accelerated electron, and deposit out as sodium atoms.

The above-described process has found limited application, primarily inthe preparation of photoelectric tubes and the like. One of theprincipal reasons for this limited application is that the process isrestricted to the deposition of metals on the interior surfaces of glassenvelopes that are capable of being fitted with filaments, evacuated,and immersed in molten salt baths, The restriction on the shape of theglass member is especially severe, and precludes many desirableapplications.

Accordingly, an object of this invention is to provide an electron-beamelectrolysis which is not restricted to envelope-shaped glass members.

Another object is to provide an electron-beam electrolysis which doesnot require the use of the molten salt bath of the prior art.

Another object is to provide an electron-beam apparatus and method forelectrolyzing any material which at a predetermined elevated temperatureis a substantially solid electrolytic conductor.

A further object is to provide an electron-beam apparatus and method fordepositing metal coatings on selected surfaces of shaped bodies ofglass, ceramic, solid salt or the like.

A still further object is to provide an electron-beam apparatus andmethod for obtaining metals of high purity.

These and other objects of the present invention are achieved by forminga small body of a material which at a predetermined elevated temperatureis a substantially solid electrolytic conductor. The body iselectrically connected to a metallic anode, and the body and anode arepositioned adjacent to an electron-emissive cathode. The spacesurrounding the cathode, body, and anode is evacuated to permit the flowof electrons from the cathode to the body, and an electron-acceleratingpotential is connected between the cathode and anode. The body is heatedto the predetermined temperature at which it is a substantially solidelectrolyte, whereby the impinging electrons neutralize the mobile ionsthereof, converting them into atoms. The vacuum, temperature andaccelerating potential are maintained until the body is electrolyzed tothe desired degree. In this manner the electrolysis of the body isprecisely controlled, enabling one to modify the body as desired.

The invention will be further described with reference to theaccompanying drawing, in which the sole figure is 3,366,562 PatentedJan. 30, 1968 Zoe an elevation view, sectioned in part, of an apparatusembodying the principles of the present invention.

In the figure, the reference numeral M denotes an elongated cylindricalvacuum chamber consisting of separable upper and lower portions 11 and12, respectively. The portions 11 and 12 preferably are constructed ofglass or other transparent material, and are provided with circularground-glass flanges l3 and 14, respectively. The upper portion 11 has apair of short, integrally-formed tubes 15, 16 extending verticallyupwardly therefrom, and an integrally-formed horizontal arm 17 thatconnects the vacuum chamber 10 to a vacuum diffusion pump 18. Extendingvertically downwardly from the lower portion 12 of the vacuum chamber 10is a single integrally-formed short tube 19.

The tubes 15 and 16 are fitted with conventional feedthrough vacuumseals 20 and 21 which slidably carry a pair of rods 22, 23 of copper orother highly-conductive metal. The rods 22, 23 extend into the lowerportion of 12 of the vacuum chamber 10 and electrically connect to anelectron-emissive cathode 24. The cathode 24 advantageously consists ofa helical coil of wire 25 the ends of which are screwed, clamped, orotherwise fastened to the rods 22, 23. The wire 25 preferably comprisesa material suitable for providing incandescent filaments, such astungsten, thoriated tungsten or the like.

The rods 22, 23 at their upper ends are connected by conductors 26 to anadjustable electrical current source 27 capable of supplying suflicientcurrent to heat the coil 25 to incandescence. The current supplied bysource 27 may be either direct or alternating current.

The tube 19 extending downwardly from the vacuum chamber 10 is providedwith a conventional feed-through vacuum seal 28 that slidably supportsan electricallyinsulative tube 29. A wire 36 extends through the tube 29and is connected, as by brazing, to the underside of a flat, horizontal,metallic anode 31. Thermally disposed against the anode 3]. is anelectrical temperature sensor 32 such as thermocouple, thermistor, orthe like. A pair of insulated conductors 33 extend from the temperaturesensor 32 through the insulative tube 29 to an associated electricaltemperature indicating device 34!. The conductors 33 are retained in thetube 29 by any convenient means, for example, by friction or by a hightemperature cement.

The tube 29 preferably is ceramic, and the anode 31 preferably isplatinum or other metal capable of fusion to the ceramic tube 2%. Thetop of tube 29 is fused to the underside of the anode 31 so as tomaintain a vacuum in chamber 10.

The anode 31 is electrically connected to the underside of a small body35 of material to be electrolyzed. The body 35 covers the top surface ofthe anode 31 and preferably extends down the vertical sides of theanode, so as to prevent the electrons emitted by cathode 24 fromdirectly contacting the anode. The body 35 may be formed in anyconvenient manner, as by cutting, molding, or the like, from any of thewell-known materials such as glasses, ceramics, salts and the like,which at predeterminable elevated temperatures conduct electrolytically(ionically) and yet remain substantially solid. The determination ofsuitable materials and their solid-conduction temperatures may readilybe effected by those skilled in the art.

A particularly convenient method of shaping the body 35 and connectingit to the anode 31 comprises melting the material of the body 35 andcasting the material about the anode 31, whereby the material makes goodelectrical contact with the anode 31 along the top and side surfacesthereof, as illustrated in the figure.

An adjustable high voltage source 37 and milliammeter 38 are connectedin series between one of the rods 22, 23, for example, rod 22 and thewire 30 attached to the anode 31. The voltage source 37 may bedirect-current, in which case the anode wire 30 should be connected tothe positive lead of the source. Alternatively, the voltage source 37may be alternating-current, since the cathode 24 and anode 31 areinherently rectifying. In either case, the voltage of the source 37should be adjustable from several hundred to several thousand volts,preferably about 100-3000 volts.

To raise the body 35 to its predetermined solid-conduction temperature,the lower portion 12 of the vacuum chamber 10 is Wound with a suitableheating coil 41 comprising an induction coil, resistance coil, or thelike. An adjustable current source 42 is connected to the coil 41 toenergize the coil.

. Inthe operation of the apparatus shown in the figure, the vacuumchamber 10 initially is separated into the upper and lower portions 11,12. The anode 31 is removed from the lower portion 12 by disconnectingthe Wires 30 and 33 from their associated elements 38 and 34,respectively, and withdrawing the ceramic tube 29 upwardly from thefeed-through vacuum seal 28. The body 35 is then firmly attached to theanode 31, and the ceramic tube 29 is replaced in the seal 28. The upperand lower portions 11 and 12 are mated at the flanges 13, 14, and thespacing between the top of the body 35 and the coil 25 is adjusted toabout 1-10 cms. and preferably about 2-5 cms. by manually moving theceramic tube 29 in its seal 28, and/or the rods 22, 23 in their seals21, 22. The vacuum pump 13 is turned on and operated until the vacuum inchamber 10 is about 10- -10- torr, as indicated on a suitable vacuumgauge 43 connected to the chamber 10. The adjustable current source 27is connected to the rods 22, 23 via the leads 26, and the source 27 isturned on and adjusted until the coil 25 is brightly incandescent. Inmany instances the heat produced by the coil 25 is sufiicient to raisethe body 35 to its predetermined solid-conduction temperature, asmeasured by the sensor 32 and indicating device 34. If the indicatedtemperature approximately equals the predetermined temperature, the highvoltage source 37 and milliammeter 38 are connected between the rod 22and the anode Wire 30. The source 37 is turned on and adjusted toproduce an electrolysis current of about 1-100 milliamperes, preferablyabout -50 milliamperes, depending on the area of the body 35 beingelectrolyzed, and the electron-emitting properties of the coil 25. Ifthe indicated temperature of body 35 due to the heat of the cathode coil25 does not approximate the solid-conduction temperature of the body,the heating coil 41 is connected to its source 42, which is then turnedon and adjusted to supply sufficient heat to the body 35 to raise it tothe solid-conduction temperature.

The vacuum in the chamber 10 is maintained at about 10- --10 torr duringthe electrolysis, while the temperature of the body 35 is maintained atthe solid-conduction temperature, by adjusting the heating source 42 ifnecessary. The entire chamber 10 preferably is air-cooled by means of afan or the like 45 to dissipate any excessive heat and protect the glassof chamber 10. The cathode coil 25 is maintained at a brightincandescence, and the electrolysis current is maintained at about 10-50milliamperes by adjusting the high voltage source 37 as required. As theelectrolysis proceeds, a metal film forms on the top surface of the body35, if the material of the body is a glass, ceramic, salt or the like.It is believed that the metal forms from the combination of electrons,that are boiled from the cathode coil 25 and accelerated by the highvoltage of source 37 to the body 35, and the mobile metal ions in thebody 35 that is at its solidconduction temperature. An electrodereaction also occurs at the interface between the body 35 and anode 31,as evidenced by a corrosion of the body 35 in this region. If gases areproduced they are withdrawn from the chamber 10 by the vacuum pump 18,and may be recovered thereat by any of the means well known in the art.

The present invention contemplates the formation of thin uniform layersof metals on the top surface of the body 35, to provide metalliccoatings on ceramic, glass, or other nonmetallic bodies. It is furthercontemplated that the shape of the coating may be controlled by sweepingthe electron beam projected from the cathode coil 25 to the anode 31.The electrostatic and electromagnetic means for accomplishing suchsweeping are well known in the art and may readily be applied to thepresent invention by those skilled in the art.

Since the present invention enables one to electrolyze solid" materialsinto metals without contacting the metal with an electrode, theinvention may provide a method of obtaining metals, especially the rareearth metals, in a high purity state. It is contemplated, in thisconnection, that means he provided to continually scrape the depositedmetal from the body, so as to enable the electron beam to continuallysee the body being electrolyzed.

In using the apparatus illustrated in the drawing and following theprocedure described above: (1) a small solid body of silver chloride waselectrolyzed and a coating of silver on the body was obtained; (2) asmall solid body of nickel chloride dissolved in potassium chloride waselectrolyzed and a coating of nickel on the body was obtained; and (3) asmall solid body of zirconium oxide was electrolyzed and a coating ofzirconium on the body was obtained.

While the present invention has been described by way of specificillustrative embodiments, it will readily be apparent to those skilledin the art that many modifications and variations may be effected withinthe scope and spirit of the invention. Accordingly it is intended thatthe invention cover all such modifications and variations as fall withinthe meaning of the appended claims.

What is claimed is:

1. The method of electrolyzing a solid material which at a predeterminedelevated temperature is a substantially solid ionically conductivematerial, comprising the steps of:

(a) electrically connecting a small body of said material to a metallicanode,

(b) positioning said body and anode from about 2-5 centimeters from anelectron-eniissive cathode,

(c) evacuating the space surrounding said cathode, body and anode to apressure of about 10- -10- torr,

(d) heating said body to said predetermined temperature,

(e) applying an electron-accelerating potential between said cathode andanode, and

(f) maintaining said vacuum, predetermined temperature, and potentialuntil said body is electrolyzed to a desired degree.

2. The method set forth in claim 1, wherein said solid material is amember of the class consisting of glass, ceramic, and salt.

3. The method set forth in claim 1, wherein said electron-acceleratingpotential is about -3000 volts.

References Cited UNITED STATES PATENTS 3,267,015 8/1966 Morley 204l923,305,473 2/1967 Moseson 204298 3,329,601 7/1967 Mattox 204-1923,336,211 8/1967 Mayer 204192 HOWARD S. WILLIAMS, Primary Examiner.

ROBERT K. MIHALEK, Examiner.

1. THE METHOD OF ELECTROLYZING A SOLID MATERIAL WHICH AT A PREDETERMINED ELEVATED TEMPERATURE IS A SUBSTANTIALLY SOLID IONICALLY CONDUCTIVE MATERIAL, COMPRISING THE STEPS OF: (A) ELECTRICALLY CONNECTING A SMALL BODY OF SAID MATERIAL TO A METALLIC ANODE, (B) POSITIONING SAID BODY AND ANODE FROM ABOUT 2-5 CENTIMETERS FROM AN ELECTRON-EMISSIVE CATHODE, (C) EVACUATING THE SPACE SURROUNDING SAID CATHODE, BODY AND ANODE TO A PRESSURE OF ABOUT 10-4-10-5 TORR, (D) HEATING SAID BODY TO SAID PREDETERMINED TEMPERATURE, (E) APPLYING AN ELECTRON-ACCELERATING POTENTIAL BETWEEN SAID CATHODE AND ANODE, AND (F) MAINTAINING SAID VACUUM, PREDETERMINED TEMPERATURE, AND POTENTIAL UNTIL SAID BODY IS ELECTROLYZED TO A DESIRED DEGREE. 